Fluidfoil section

ABSTRACT

Airfoil sections having improved lift characteristics are described for use as propeller blades for air or marine craft for wings of aircraft for hydrofoil sections of hydrofoil vessels and for rotor blades in compressor stages of gas turbine engines. The improved section is characterized by a planar upper portion and convex face extending rearwardly of the leading edge for approximately one-third of the chord length of the section whereupon the face assumes a planar shape terminating at the trailing edge in either convergent or parallel relation with the upper surface of the section. The camber line of the trailing edge may be deflected in a direction away from the upper surface at an angle to the mean camber line of the section. Such improved airfoils provide lift by generation of a large positive pressure on the face of the section and only a small negative pressure on the upper surface of the section.

United States Patent Phillips [54] FLUIDFOIL SECTION [72] Inventor:Adrian Phillips, 14 Deer Park Cresent, Toronto, Ontario, Canada [22]Filed: Dec. 10, 1970 [21] Appl. No.: 96,851

Related US. Application Data [63] Continuation-impart of Ser. No.11,382, Feb.

DIRECTION OF ROTATION 1 51 Oct. 10,1972

Primary Examiner-Everette A. Powell, Jr. Attorney-Arne l. Fors, Frank I.Piper and Brian Thorpe ABSTRACT Airfoil sections having improved liftcharacteristics are described for use as propeller blades for air ormarine craft for wings of aircraft for hydrofoil sections of hydrofoilvessels and for rotor blades in compressor stages of gas turbineengines. The improved section is characterized by a planar upper portionand convex face extending rearwardly of the leading edge forapproximately one-third of the chord length of the section whereupon theface assumes a planar shape terminating at the trailing edge in eitherconvergent or parallel relation with the upper surface of the section.The camber line of the trailing edge may be deflected in a directionaway from the upper surface at an angle to the mean camber line of thesection. Such improved airfoils provide lift by generation of a largepositive pressure on the face of the section and only a small negativepressure on the upper surface of the section.

13 Claims, 6 Drawing Figures CHORD LINE PATENTEDHBI 10 m2 3.697.193

SHEET 1 [IF 2 PITCHILINEI .CHORD LINE '14 FIG 1 (PRIOR ART) VESSEL VELOCT Y Vv v BLADE VELOCITY VB ROTATION H K\ i ll 14 FIG. 2 I" (PRIOR ART) EINCREASED PRESSURE CHORD LINE P ITCH LINE DIRECTION OF ROTATION -I 8 2DECREASED PRESSURE INCREASED PRESSURE FIG. 4

INVENTOR. ADRIAN PHILLIPS Agent FLUIDFOIL SECTION This application isfiled as a continuation-in-part to my co-pending US. Pat. applicationSer. No. 11,382 filed Feb. 16, 1970 and entitled Improved Propeller.

The present invention relates to an airfoil section having improved liftcharacteristics and it is contemplated that the subject airfoil may haveapplication in the design of propulsive propellers for both air andmarine craft, for wing sections of aircraft and hydrofoil vessels andfor the rotor blades of gas turbine compressor stages.

It is, of course, known that all airfoil sections are designed onaerodynamic principles whereby the face or rearward surface of thesection is usually flat and the upper or forward surface is convexproviding the section with a positive camber. With reference to the useof such airfoil sections in propulsive propeller assemblies, it is knownthat, in operation, rotation of such a propeller in a fluid medium abouta rotary hub upon which the propeller blades are mounted, causes them tomove through the fluid at a pitch angle relative to the plane ofrotation of the propeller. Such rotation results in the generation of apositive pressure on the flat face of the blade and a negative pressureover the upper surface of the blade, the latter negative pressureproviding about two-thirds of the thrust obtained. Such propeller bladeusually is evenly cambered between its leading and trailing edges inorder to reduce peak levels of negative pressure over the upper convexsurface.

A number of major problems can arise from the application of theseprinciples and in particular, it is observed that the pressure dropinduced over the upper surface of such propeller blades can promoteturbulence (or cavitation as it is termed in marine useage),particularly at high blade speeds. Such turbulence, or cavitation, canand often does result in blade damage, undesirable vibration and thecreation of excessive drag characteristics.

The downwash caused at the trailing edges of the blades by the convexcontour of the blade upper surface results in an induced angle of attackof the blade relative to the direction of flow of the fluid medium. Thisinduced angle of attack produces a drag component which acts inopposition to the torque provided to the propeller shaft to impederotation of the propeller through the fluid medium.

The foregoing remarks are equally applicable to airfoil section rotorblades used in the compressor stages of a gas turbine engine, and alsoto aircraft wings and the foils of hydrofoil vessels. In all suchsections, lift is provided, as aforesaid, through the creation ofnegative pressure over the upper convex surface of the section and alesser positive pressure on the section face. Although the resultantlift is caused by the acceleration of the fluid medium in a downwarddirection, a pressure drop is created over the section of the surfacecausing the fluidstream to be drawn primarily in an upward directionprior to its being persuaded to pursue a downward course by the shape ofthe airfoil section.

This method of producing lift has a number of inherent problems, theprimary ones being a. the ability of the convex upper surface of thesection to persuade the fluid flow to follow its upper con tour underlaminar flow conditions, or even under turbulent flow conditions whenthe rotation of acceleration of the fluid about the upper surface causesflow separation. This condition, when aggravated, causes a completebreak-down of the fluid flow producing a stall condition at which pointlift rapidly diminishes.

b. the rotational velocity around the upper surface of the sectioncauses the downwash at the trailing edge which, in turn, results in aninduced angle of attack and commensurate induced drag component. Inaddition, trailing edge vortices occur as the upper and lower flowstreams (at different pressures and velocities) meet immediatelyrearward of the trailing edge.

e. the fact that the incident fluid stream is sucked upwards towards thelow pressure upper surface prior to being induced to assume a downwarddirection at the trailing edge, implies that work has been done to raisethe fluid stream and must be deducted from the work done to direct thefluid stream in a downward direction in order to arrive at the trueresultant lift force.

d. a conventional airfoil section is basically unstable. As the majorityof the lift is produced by the creation of the negative pressure overthe convex upper surface towards the leading edge, any increase in lifttends to accentuate the moment already trying to raise the leading edge,and, if unchecked, this wouldresult in a larger angle of attack, greaterlift and the eventual onset of a stall condition.

It is a broad object of the present invention to provide animproved'airfoil section having improved lift characteristics which willproduce the major portion of thrust from positive pressure exerted by afluid medium on its face instead of utilizing negative pressure on itsupper surface.

It is another object of the invention to provide such an airfoil sectionproviding maximum fluid displacement in a restricted zone in proximityto, and coextensive with, the leading edge of the section, therebypermitting increase of the area of planar surface desirable forstreamlining fluid flow in order to reduce turbulence due to trailingedge vortices normally inherent in conventional airfoil section design.This substantial elimination of trailing edge vortices is effective inminimizing the induced angle of attack and consequently minimizinginduced drag and the occurence of a stall condition.

In accordance with the invention, there is provided an airfoil sectionhaving a leading edge and a trailing edge and an upper surface and aface, said face of the section having a convex shape commencing at thele ading edge and terminating intermediate the leading edge and trailingedge, whereupon the face assumes a planar shape extending over at leastpart of said face forward of the trailing edge; said upper surface ofthe section having a substantially planar shape between the leading edgeand the trailing edge, whereby the major portion of lift provided by thesection moving through a fluid medium is produced by positive pressureexerted on said face of the section by said medium.

In one form of said airfoil section according to the invention, theplanar shape of said face extends continuously from the said terminationof the convex shape to the trailing edge of the section, whilst inanother form, said planar shape of said face terminates intermediate theleading and trailing edges of the section and said face has a generallyconcave shape extending from said termination of said planar shape tothe trailing edge of the section. In addition, in either of the twoforms aforementioned, the camber line of the trailing edge of thesection may be deflected in a direction away from the upper surface atan angle to the mean camber line of the section.

It is believed that the aforementioned design of airfoil section givesrise to the following advantages.

a. By creating a relatively flat upper surface of the section, the roleof the upper surface becomes of significantly less importance than theface with respect to the lift generating ability of the section. Thissubstantially reduces the presence of any rotational acceleration" ofthe fluid medium over the upper surface.

b. Down-wash is reduced to a minimum by virtue of the upper surfacebeing flat and the rotational acceleration of the fluid stream acrossthe upper surface being substantially reduced. In addition, to attractthe incident fluid stream to the face of the leading edge, as opposed tothe upper surface, said face has a convex shape commencing at theleading edge, thereby not only causing a localized drop in pressure toattract the incident flow stream, but also reducing the pressure drag atthe leading edge. Such effects create fluid pressure on the face of thesection substantially at and rearward of mid-chord where the face has aplanar shape in accordance with the invention, thereby producingincreased lift.

c. As the majority of lift forces generated are on the center andrearward portions of the face of the section, the resultant lift forceis rearward of the center of gravity of the section, thereby insuringstability. If excessive lif t is experienced, the resulting moment actsto return the section to an attitude of balanced equilibrium.

Other feature of the invention will become apparent from the hereinafterfollowing description of the parts, principles and elements thereofgiven herein solely by way of example with reference to the accompanyingdrawings, wherein like reference numerals refer to like parts throughoutthe several views and wherein:

FIG. I is a transverse section of a conventional airfoil section, asutilized in a propulsive propeller for air or marine craft;

FIG. 2 is a graphical illustration of pressure distribution about theblade shown in FIG. 1, as the blade is pivoted through a fluid mediumabout a propeller hub;

FIG. 3 is a transverse section of a propeller blade constructed inaccordance with the present invention;

FIG. 4 is a graphical illustration of pressure distribution about theblade shown in FIG. 3, as the blade is pivoted through a fluid mediumabout a propeller hub;

FIG. 5 is an enlarged transverse section of an airfoil constructed inaccordance with the invention, similar to the section utilized in thepropeller blade of FIG. 3 showing a modified face of the section at thetrailing edge, and also illustrating in graphical form the pressuredistribution about the section as it is moved through a fluid medium;and

FIG. 6 is a transverse section of a modified form of the airfoil shownin FIG. 5, having a concave section forward of its trailing edge.

FIGS. 1 to 4 of the drawings relate to utilization of the subjectairfoil section in the propulsive propeller for a maring craft, althoughit should be understood that the following principales are generallyapplicable to such a design of airfoil section utilized also in thepropulsive propellers of aircraft and for wing sections of aircraft, thefoils of hydrofoil vessels and for the rotor blades of the compressorstages in a gas turbine engine.

With reference to FIG. 1 of the drawing, a conventional marine propellerblade is arranged at a pitch angle P relative to the direction ofrotation of the blade measured from the blade pitch line, which iscoincident with the chord line formed by the rearward surface 10 of theblade. It will be understood that the vectors indicated relate bladevelocity Vb, in the direction of rotation of the propeller, to thevessel velocity Vv, sub tending an angle B and hypotenuse Vr forrelative water velocity. The angle a indicates the blade angle ofattack.

FIG. 2 shows the sectional area of decreased pressure coextensive withthe convex upper surface 14 of the blade illustrated in FIG. 1.Approximately twothirds of the total lift affecting the blade is derivedfrom the said negative pressure resulting in undesirablecharacteristics, such as cavitation and turbulence inherent inconventional blade design.

FIG. 3 illustrates a blade section in accordance with the presentinvention in which the chord line indicated connects the blade trailingedge 18 to the blade leading edge 20. The pitch line coincides with theflat portion 24 of planar shape on the face of the blade aft of theconvex shape portion 26, which commences at the leadingedge 20 andterminates at a longitudinal line designated by numeral 28. The convexshape portion 26 is shown to extend rearward from the leading edgeapproximately one-third of the chord length, while, although the lengthof said portion 26 can be varied to some small degree, it is preferableto maintain a relatively long planar portion 24 to minimize turbulenceand trailing edge vortices. In this embodiment, said planar shapeportion 24 extends continuously rearwardly of the blade face from thetermination 28 of the convex shape portion 26 to the trailing edge 18 ofthe blade. The radius of curvature of the convex portion 26 can bevaried for particular propeller applications depending primarily on thethickness ratio of the blade section.

The upper surface of the blade is substantially planar between theleading edge 20 and trailing edge 18 having a flat portion 30 and aslightly convex portion 32 extending rearwardly from the leading edge 20on the upper surface. The upper surface convex portion 32 is joined tothe face convex portion 26 by a rounded leading edge 20.

It will be understood that the upper surface of the section can becontinuously planar with no convex portions as designated by numeral 32,and in any event, such convex portion 32 will only extend rearwardlyfrom the leading edge 20 for approximately one-sixth of the chord lengthbetween the leading edge and trailing edge of the blade.

FIG. 4 illustrates the relatively small area of decreased pressure onthe upper surface of the blade and the relatively large area ofincreased pressure coextensive with the convex and planar shapedportions 26-24 on the face of the blade. As the majority of thrust isprovided by this increased pressure, i.e., positive pressure, cavitationand turbulence due to negative pressure is minimized. The flat portions24 and 30 on the face and upper surface of the blade respectively extendto the trailing edge 18 in convergent relation for permitting thenegative and positive pressures to return to static pressure in auniform manner from the trailing edge 18 of the blade, therebyminimizing turbulence and trailing edge vortices. To assist inestablishing this uniform return to static pressure, the upper surfaceand face of the blade squared 011" at the trailing edge 18 as distinctfrom the pointed configuration shown in FIGS. 3 and 4.

FIG. 5 of the drawings illustrates an airfoil section in accordance withthe invention of a form similar to that shown in FIGS. 3 and 4, butwherein the radius of curvature of the convex portion 26 on the face isconsiderably greater. Such a section may also find application in thedesign of propulsive propellers for both air and marine craft, for wingsections for aircraft, for

' hydrofoil sections for hydrofoil vessels and for the rotor blades ofthe compressor stages of gas turbine engines.

The airfoil section shown in FIG. 5 is provided with the convex shapeportion 26 on its face extending rearwardly from the.leading edge 20 andterminating at position 28 approximately one-third of the chord lengthaft of the leading edge, whereupon the face assumes the planar shape 24extending towards the trailing edge 18. Said planar shape24extends in adirection convergent to the upper surface for approximately onehalf thechord length to a position indicated at 34 whereupon it assumes aconcave shape and a further planar shape 36 parallel to the uppersurface. This planar shape portion 36 thus occupies approximatelyone-sixth of said chord length. The upper surface of the section may beslightly convex, as shown at 32, extending rearwardly on the uppersurface aft of the leading edge 20 for a distance approximatelyone-sixth of the chord length, and thereafter assuming the planar shapeextending continuously to the trailing edge 18.

In this design, the majority of thrust is again provided by increasedpressure, i.e. positive pressure, on the face of the section, and due tothe difference in radius of curvature of the convex portion 26 of thesection face, as compared with that shown in FIG. 3, the area ofincreased pressure is shifted further rearward of the section to aposition further rearward of the center of gravity thereof, therebyensuring greater stability to the section.

Such parallel relation between the upper surface and face for a distanceapproximately one-sixth of the chord length forward of the trailing edge18 permits the negative and positive pressures to return to staticpressure in a uniform manner from the trailing edge 18 of the section.

Another form of the subject airfoil section is shown in FIG. 6 of thedrawings wherein the camber line of the trailing edge on both the uppersurface and the face is deflected away from the upper surface at anangle to the mean camber line of the section. In this embodiment, it ispreferred that the convex portion 26 of the face extend rearward of theleading edge for approximately one-third of the chord length whereuponit assumes the planar shape 24 extending for a further one half of thechord length distance. This planar shape portion 24 then terminates atthe position indicated by reference numeral 38 whereupon the faceassumes a concave configuration in a direction towards the trailing edge18. Similarly, the planar shape of the upper surface ;terminates at aposition forward of the trailing edge 18 of the section and is curved tocorrespond to the curvature of the blade face. Thus, the upper surfaceof the section assumes a convex shape 42 in concentric relation with theconcave shape 40 of the face whereby the camber line of the trailingedge of the section on both said upper surface and face is deflected ina direction away from the upper surface at an angle to the mean camberline of the section. From the proportions given hereinbefore, it will beappreciated that such camber line deflection extends forwardly of thetrailing edge 18 for a distance of approximately onesixth of the chordlength and the concentric relation of the curvature between the convexshape 42 of the upper surface and the concave shape 40 of the face willagain pemiit the negative and positive pressures to return to staticpressure in a uniform manner from the trailing edge 18 of the section.

In this form of the invention, a large area of increased positivepressure is again produced on the section face and due to the provisionsof the camber line deflection, the center of such pressure is moved evenfurther rearward relative to the center of gravity of the section ascompared with the area of pressure indicated in the FIG. 5 embodiment.It will, of course, be appreciated that variation in the rate of camberadjacent the trailing edge 18 will vary the position and area of theincreased pressure region on the face of the section; increased rate ofcamber generally shifting the center of positive pressure furtherrearward of the center of gravity of the section for insuring greaterstability thereto.

What I claim as new and desire to protect by Letters Patent of theUnited States is:

l. A fluidfoil section having a leading edge and a trailing edge and anupper surface and a face,

said face being the high pressure working surface,

said face of said section having a convex shape commencing at theleading edge and terminating intermediate the leading edge and trailingedge whereupon the face assumes a planar shape extending over at leastpart of said face rearward of said termination, said upper surface ofthe section having a substantially planar shape extending from theleading edge to adjacent the trailing edge whereby the major portion oflift provided by the section moving through a fluid medium is producedby positive pressure exerted on said face of the section by said medium.

2. A fluidfoil section as claimed in claim 1 wherein:

said planar shape of both said upper surface and face extends to thetrailing edge of the section, said upper surface and face beingconvergent towards one another at the trailing edge providing awedgeshaped cross-sectional configuration thereto.

3. A fluidfoil section as claimed in claim 1 wherein:

said planar shape of the upper surface extends to the trailing edge ofthe section,

said planar edge of the face extends rearwardly from said termination ofsaid convex shape to a position forward of the trailing edge in a planeconvergent towards the upper surface whereupon said face assumes afurther planar shape parallel to said upper surface at the trailingedge.

4. A fluidfoil section as claimed in claim 3 wherein:

said face assumes a concave shape intermediate those said planar shapesof the face which are respectively convergent towards and parallel tosaid upper surface.

5. A fluidfoil section as claimed in claim 1 wherein:

the camber line of the trailing edge of said section on both said uppersurface and face thereof is deflected in a direction away from the uppersurface at an angle to the mean camber line of the section.

6. A fluidfoil section as claimed in claim wherein:

said face has a said convex shape for approximately one-third of thechord length between the leading edge and trailing edge thereof and,

said camber line deflection extends forward of said trailing edge forapproximately one-sixth of the said chord length.

7. A fluidfoil section as claimed in claim 2 wherein:

said face has a said convex shape for approximately one-third of thechord length between the leading edge and trailing edge thereof and,

said upper surface of the section has a convex shape extending from theleading edge for approximately one-sixth of said chord length.

8. A fluidfoil section as claimed in claim 3 wherein:

said face has a said convex shape for approximately one-third of thechord length between the leading edge and trailing edge thereof, saidplanar shape extends for approximately one-half of said chord lengthafter the tennination of said convex shape and,

said further planar shape extends approximately onesixth of said chordlength in said parallel relation with said upper surface.

9. A fluidfoil section as claimed in claim 8 wherein:

said upper surface of the section has a convex shape extending from theleading edge for approximately one-sixth of said chord length.

10. A fluidfoil section as claimed in claim 1 wherein:

said planar shape of both the upper surface and face terminate at aposition forward of the trailing edge and,

said upper surface and face are curved aft of said position towards thetrailing edge providing a convex shape to the upper surface and aconcentric concave shape to the face whereby the camber line of thetrailing edge on both said upper surface and face is deflected in adirection away from the upper surface at an angle to the mean camberline of the section.

11. A fluidfoil section as claimed in claim 10 wherein:

said camber line deflection extends forward of said trailing edge forapproximately one-sixth of the chord length between the leading edge andtrailing edge thereof.

12. A fluidfoil section as claimed in claim 11 wherein:

wherein:

said upper surface of the section has a convex shape extending from theleading edge for approximately one-sixth of said chord length.

1. A fluidfoil section having a leading edge and a trailing edge and anupper surface and a face, said face being the high pressure workingsurface, said face of said section having a convex shape commencing atthe leading edge and terminating intermediate the leading edge andtrailing edge whereupon the face assumes a planar shape extending overat least part of said face rearward of said termination, said uppersurface of the section having a substantially planar shape extendingfrom the leading edge to adjacent the trailing edge whereby the majorportion of lift provided by the section moving through a fluid medium isproduced by positive pressure exerted on said face of the section bysaid medium.
 2. A fluidfoil section as claimed in claim 1 wherein: saidplanar shape of both said upper surface and face extends to the trailingedge of the section, said upper surface and face being convergenttowards one another at the trailing edge providing a wedge-shapedcross-sectional configuration thereto.
 3. A fluidfoil section as claimedin claim 1 wherein: said planar shape of the upper surface extends tothe trailing edge of the section, said planar edge of the face extendsrearwardly from said termination of said convex shape to a positionforward of the trailing edge in a plane convergent towards the uppersurface whereupon said face assumes a further planar shape parallel tosaid upper surface at the trailing edge.
 4. A fluidfoil section asclaimed in claim 3 wherein: said face assumes a concave shapeintermediate those said planar shapes of the face which are respectivelyconvergent towards and parallel to said upper surface.
 5. A fluidfoilsection as claimed in claim 1 wherein: the camber line of the trailingedge of said section on both said upper surface and face thereof isdeflected in a direction away from the upper surface at an angle to themean camber line of the section.
 6. A fluidfoil section as claimed inclaim 5 wherein: said face has a said convex shape for approximatelyone-third of the chord length between the leading edge and trailing edgethereof and, said camber line deflection extends forward of saidtrailing edge for approximately one-sixth of the said chord length.
 7. Afluidfoil section as claimed in claim 2 wherein: said face has a saidconvex shape for approximately one-third of the chord length between theleading edge and trailing edge thereof and, said upper surface of thesection has a convex shape extending from the leading edge forapproximately one-sixth of said chord length.
 8. A fluidfoil section asclaimed in claim 3 wherein: said face has a said convex shape forapproximately one-third of the chord length between the leading edge andtrailing edge thereof, said planar shape extends for approximatelyone-half of said chord length after the termination of said convex shapeand, said further planar shape extends approximately one-sixth of saidchord length in said parallel relation with said upper surface.
 9. Afluidfoil section as claimed in claim 8 wherein: said upper surface ofthe section has a convex shape extending from the leading edge forapproximately one-sixth of said chord length.
 10. A fluidfoil section asclaimed in claim 1 wherein: said planar shape of both the upper surfaceand face terminate at a position forward of the trailing edge and, saidupper surface and face are curved aft of said position towards thetrailing edge providing a convex shape to the upper surface and aconcentric concave shape to the face whereby the camber line of thetrailing edge on both said upper surface and face is deflected in adirection away from the uppeR surface at an angle to the mean camberline of the section.
 11. A fluidfoil section as claimed in claim 10wherein: said camber line deflection extends forward of said trailingedge for approximately one-sixth of the chord length between the leadingedge and trailing edge thereof.
 12. A fluidfoil section as claimed inclaim 11 wherein: said face has a said convex shape for approximatelyone-third of the chord length between the leading edge and the trailingedge thereof and, said planar shape extends for approximately one-halfof said chord length aft of the termination of said convex shape.
 13. Afluidfoil section as claimed in claim 12 wherein: said upper surface ofthe section has a convex shape extending from the leading edge forapproximately one-sixth of said chord length.